1. Field of Invention
The invention relates to a driver circuit of light sources, particularly of the LED type, and to a front or rear vehicle light, provided with such a driver circuit of light sources to make one or more lamps of the vehicle light itself, such as a stop lamp, a front or rear parking lamp, a front or rear turn signal lamp, a reversing lamp, a rear fog lamp, a front or rear side parking lamp, a low beam lamp, a high beam lamp, a daylight running lamp (DRL), a fog lamp, a cornering lamp, and the like.
2. Description of the Related Art
A driver circuit of light sources is known in the art, including a plurality of light sources, particularly of the LED type, structured so as to emit light when subjected to a power supply voltage, wherein the driver circuit of the light sources is configured to position the plurality of light sources in at least a first and a second matrix arrangement of n rows×m columns, upon the variation of the power supply voltage.
The plurality of light sources of the driver circuit is further able to absorb an overall electric current defined by a constant electric current value In for each of said first and second matrix arrangement of the light sources, multiplied by a number of m columns of the matrix arrangement of the light sources. The number of columns ml of the matrix of the first matrix arrangement of the light sources is greater than the number of columns m2 of the matrix of the second matrix arrangement of the light sources. Consequently, the number of light sources of each column of the first matrix arrangement of the light sources is smaller than that of each column of the second matrix arrangement of the light sources. Thus, the first matrix arrangement of the light sources requires a power supply voltage lower than that of the second matrix arrangement of the light sources to turn on the plurality of light sources. Consequently, the plurality of light sources arranged according to the first matrix arrangement can emit light at a lower power supply voltage than the second matrix arrangement of light sources, without encountering a flickering of light itself, to the detriment, however, of a greater electric power consumption than the second matrix arrangement of the light sources. In fact, the electric power consumption of the light sources arranged in a matrix depends on the number of columns m of the LED matrix.
Specifically, the electric power consumption is given by the formula:
P(V)=m×In×V, wherein P(V) is the electric power absorbed by the plurality of light sources, m is the number of columns, In is the constant electric current, and V is the variable power supply voltage.
For the above reason, the transition between the first and the second matrix arrangement of the light sources (namely the transition from the matrix arrangement of the light sources with more columns between the two) to that with fewer columns between the two, needs to occur at a value of power supply voltage as small as possible.
With reference to FIG. 1, by way of example, the electric power P(V) dissipated by the light sources arranged with a first matrix arrangement of two rows and six columns and a second matrix arrangement of three rows and four columns A polyline is obtained by plotting the electric power P(V), given by a first slope segment 6In, a step in vertical descent, at the power supply voltage in which the driver circuit of the light sources switches from the first to the second arrangement of the light sources, and a second slope segment 4In.
However, the above-mentioned driver circuit of light sources, to which reference will be made in the continuation of the description with the expression “dynamic matrix”, has some drawbacks. In fact, the number of light sources needs to be dividable by the number of rows, or columns, of the first and second matrix arrangement of the light sources, respectively. For example, eighteen light sources can be arranged in a matrix in a first matrix arrangement of light sources of six rows by three columns, and in a second matrix arrangement of light sources of three rows by six columns, since the eighteen light sources are dividable by the number of rows, or columns, of both the first and the second matrix arrangement of the light sources. However, the eighteen light sources cannot be arranged in a matrix arrangement of light sources having, for example, five rows, since the eighteen light sources are not dividable by the number of rows in the matrix arrangement of the light sources.
A further drawback of the dynamic matrix occurs when one or more light sources in the matrix must be under-powered to emit a weaker light compared to the remaining light sources in the matrix. This need can occur, for example, in the field of automotive lights, where an illuminating surface of the vehicle light may include an illuminating area with low light intensity and an illuminating area with high light intensity, for photometric requirements. One might think of connecting electric resistors to the light sources affecting the illuminating area with low light intensity, so that such light sources absorb less electric current than the other light sources affecting the illuminating area with high light intensity (for example, in the first matrix arrangement of the light sources). However, the electric resistors may be connected differently to the light sources, when the driver circuit of the light sources has switched to the second matrix arrangement of the light sources, thus not guaranteeing the desired effect anymore.
Yet another drawback derives from the fact that the instant at which the transition from the first to the second arrangement of the light sources occurs (namely the transition from the matrix arrangement of the light sources with more columns to that with less columns) at a power supply voltage determined in the design phase. Such a power supply voltage is overestimated in the design phase in order to ensure the switch on of the LEDs to the detriment, however, of electric power consumption.